First, it really wouldn't be surprising if Pachycephalosaurus were partially carnivorous. Most ornithischians appear to have been plant-eaters, but there's been growing evidence they weren't all pure herbivores. Case in point the bizarre, tiny ankylosaur from the Yixian Liaoningosaurus, which seems to have some evidence of possible piscivory. I can see these guys being like Mesozoic bears or wild pigs who browse or graze at times, but also take small animals when available.

Two, we'll see if the adults likewise had these sabre-like teeth. For instance, in Limusaurus, an elaphrosaur from China, the adults have toothless beaks, but the juveniles have sharp teeth for stabbing small prey (I think that's the only case of a known vertebrate losing its teeth entirely as it ages). Point is, the number, form, and even existence of teeth can change through ontogeny.

Rebacchisaurids are becoming the new titanosaurians. There's so many new taxa being described around the globe it's crazy, although I don't think they'll reach the same pace of discovery for the simple fact they're unknown beyond the Early Late Cretaceous.

Having said that, I don't think it's surprising that rebacchisaurids, or indeed any sauropods, were found in a desert environment. In fact, I think the large size of sauropods and their kin is in part due to arid and semiarid environments among other things. Let me see the reasons why...

-Many depositional environments in which sauropods are abundant, like much of the Morrison, the Anacleto and many other sites in Patagonia, parts of Tendaguru in Tanzania, the Maevarano of Madagascar, etc., were not these lush Mesozoic jungles, but arid or seasonally arid environments.
-The world of the Early Jurassic and Triassic in which early sauropods and sauropodomorphs developed was often very arid, especially in the interior of Pangaea. The Navajo Sandstone, the Upper and Lower Elliot, etc. There would have been oases of greenery and fresh water, but there also would have been vast stretches of aeolian sand dunes and arid adapted vegetation.
-Research shows that comparatively moist, temperate ecosystems in the Middle and Late Jurassic actually have less in the way of high browsers than arid or semiarid ecosystems. This suggests many arid environments had drought-adapted trees with foliage higher up than grazers and low browsers were able to reach. High-browsing sauropods were actually better adapted to finding available vegetation in arid environments than most ornithischian herbivores.

In addition to having many biological characteristics that made them adapted to large size (fast growth, not chewing their food, hindgut digestion, air sacs like modern birds, etc.), I think the arid world of the Early Mesozoic meant that early sauropods and kin were eternal nomads constantly on the move that wandered from oasis-to-oasis, gallery forest-to-gallery forest, and eden-to-eden. Long necks and the ability to rear in some instances let them get foliage even in the worst droughts, and large size made them more able to wander through deserts and wastelands without dying of thirst or starvation than smaller dinosaurs would. The big sauropodomorphs like Ledumahadi were better able to survive such adventures than the tiniest early cousins, like Pampadromeus or Panphagia. The fact camarasaurs from the Morrison show different stable isotope signatures in between their teeth and bones, indicating they seasonally migrated to areas with cooler temperatures during warmer months, lends credence to the idea that many sauropods were on the move most of the time to serve their massive appetites. Many sauropodomorphs throughout the Mesozoic weren't just tolerant of surviving desert treks; they were adapted for it.

Even their reproductive strategies differ from those of other dinosaurs for whom data is known, and this fits their nomadic lifestyle. Maniraptoran theropods and ornithopods have evidence of brooding their eggs like birds and/or engaging in post-hatching care of their young. The sauropods of Auca Mahuevo laid their eggs in nesting grounds that were too dense to have individual parental care in the nests (although it's possible some adults patrolled the perimeters to ward against predators). Dinosaur incubation periods were longer than modern birds, ranging from a little over two months at least in Two Medicine's troodontids and Protoceratops to over five months in Hypacrosaurus. The parental strategies of many theropods and ornithischians mean that they were tied to their nests and young. Sauropods, at least in some instances, laid their eggs in foot-scraped nests or even near hot springs, buried their eggs in sediments or rotting vegetation, and left them to develop, which left their youngsters' survival to chance, but allowed them to continue their eternal voyage of wandering, browsing, digesting, and pooping.

I'm not saying all sauropods were arid-adapted either. Some lived in lush environments, but I think sauropods were actually better adapted to arid and semiarid climates than many mid-to-low browsers and grazers like ornithopods, ceratopsids, and therizinosaurs.

Interesting to see a death assemblage of hadrosaurs (the tsintaosaurin Pararhabdodon in this case) from the Tremp Formation in the Pyrenees dominated by juveniles, but the hadrosaur footprint assemblage from Alaska is dominated by adults and subadult animals. Of course, these are different hadrosaur taxa, different paleoenvironments, different climates, etc., but it's still an interesting comparison. Also interesting to see histology. Subadults were estimated to be in their sixth year of life. Young adults were in their seventh year of life, and the oldest adults were teenagers.

This is an awesome discovery regardless, but I think caution needs to be made regarding the identity of the track-makers.

There's no doubt these tracks were made by a tiny dinosaur with a dromaeosaurid-like pedal arrangement, with the first toe being reduced in sized and off the ground, the second toe enlarged and off the ground, and the third and fourth toes being the ones that the animal used to walk on.

However, while it may well likely be a tiny raptor, it may not be a dromaeosaurid at all, let alone a microraptorine like the title implies. Troodontids and many early avian dinosaurs also had raptor-like pedal arrangements, and the line between deinonychosaur and avialan is often blurry. Some taxa have been considered to be either avialans or bird-like dinosaurs (Rahonavis, Balaur, anchiornithids). And just because Microraptor has fish in its gut and teeth whose distal ends point backwards, suggesting they were catching slippery prey, it doesn't mean that if it is a dromaeosaurid that it also is a microraptorine. It's possible other dromaeosaurid clades also reached small sizes, either as adults or when they hatched from their eggs.